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What type of Sensor to use?

  1. Feb 5, 2009 #1
    I am a professional Pyrotechnician and i am designing a new firing system. I am wanting to streamline the process of our set-up and tear down of larger shows. By putting some kinda of sensor in each tube we use to shoot our shells out of to sense if the shell actually left the tube. Why I would like to do this is that after each show we have to check each tube to make sure that the shell was discharged. If it wasn't we have to remove them and send them back to the appropriate storage facility. And if I am shooting a show with 1500+ tubes that can take a while to check every tube. I am thinking that some kinda of proximity sensor would work but not sure. Each tube we use has at least a 2" thick solid wood plug in the base and would like to put the sensor in there. But again not sure that it would stand up to the lift charge from the fireworks. Any ideas?? Thanks Drew
  2. jcsd
  3. Feb 5, 2009 #2


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    Staff: Mentor

    If you can line up a bunch of the tubes in a row, I'd drill holes in the sides that all line up. The holes have to be at a level that is obstructed when there is a round in the tube, but the holes are not obstructed after the shot. Line up groups of tubes (10-20 or more) with the holes all lined up. Then after the show, just aim a laser pointer down the row, and look for the dot on the far side of the last tube.

    I think there might be too much liability in using an automated sensing system -- what if it gives a false indication of a fired round, and the round is still there and goes off in the wrong place....?
  4. Feb 5, 2009 #3
    I doubt you could drill any holes in the tubes as that will affect the height of the projectile. You also can't put just any optical or force sensor in the tube because of the concussion from the projectile would make it unreliable. I would just put red masking tape over the top of every tube after they are assembled. They will be easier to identify and should have no impact on the shells performance.
  5. Feb 5, 2009 #4


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    Use a magnetic sensor placed on the outside of each tube. I presume the shells have some type of metal in them? If so then as soon as movement of the shell is detected you will get a signal. Use two if you are concerned with reliability/liability.

    http://www.sensors-transducers.machinedesign.com/guiEdits/Content/bdeee4/bdeee4_4.aspx [Broken]

    Last edited by a moderator: May 4, 2017
  6. Feb 5, 2009 #5
    You're assuming that they contain magnetic materials. IIRC, metals such as potassium, magnesium and alkali metals which do not have magnetic properties are mostly used in fireworks displays. All of which don't have any strong magnetic properties.
  7. Feb 5, 2009 #6


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    I was assuming the shell does. I guess the OP will have to clarify.

  8. Feb 6, 2009 #7
    i think i'd go for something like a pressure switch on the bottom. like a land mine, but in reverse, with the switch making contact after the shell exits the tube. it'd need to be reasonably gas-tight to prevent fouling. i'm imagining a round disk to house the switch. hmm, i guess you go either way. probably easier to design the switch to contact when it's loaded instead of unloaded.
  9. Feb 6, 2009 #8

    A lot of companies use tape or tin foil over the top of the tubes. And it works but when you get to a larger scale of thousands of tubes it becomes costly and time consuming. Plus the clean up is a mess. I am trying to stream line the process by making it electronic.
  10. Feb 6, 2009 #9
    Here is a list of what colors are created by what compound.

    Color Compound
    Red- strontium salts, lithium salts
    lithium carbonate, Li2CO3 = red
    strontium carbonate, SrCO3 = bright red

    Orange- calcium salts
    calcium chloride, CaCl2
    calcium sulfate, CaSO4·xH2O, where x = 0,2,3,5

    Gold- incandescence of iron (with carbon),charcoal,or

    Yellow- sodium compounds sodium nitrate, NaNO3
    cryolite, Na3AlF6

    Electric White- white-hot metal, such as magnesium or aluminum
    barium oxide, BaO

    Green- barium compounds + chlorine producer
    barium chloride, BaCl+ = bright green

    Blue- copper compounds + chlorine producer
    copper acetoarsenite (Paris Green),
    Cu3As2O3Cu(C2H3O2)2 = blue
    copper (I) chloride, CuCl = turquoise blue

    Purple- mixture of strontium (red) and copper (blue)

    Silver- burning aluminum, titanium, or magnesium powder
    or flakes
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